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https://issues.apache.org/jira/browse/FLINK-4604?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15575320#comment-15575320
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Timo Walther commented on FLINK-4604:
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The problem is that the rule translates not only into {{SUM}} and {{COUNT}} but
also into {{SqlKind.SUM0}}/{{SqlSumEmptyIsZeroAggFunction}} which is not yet
supported. This means we need to adapt the {{AggregateUtil}} to support this
aggregation first. If I use the normal sum aggregator for it, I get the "Type
NULL is not supported" exception. This is bug actually a null within a {{CASE}}
expression should have a type.
> Add support for standard deviation/variance
> -------------------------------------------
>
> Key: FLINK-4604
> URL: https://issues.apache.org/jira/browse/FLINK-4604
> Project: Flink
> Issue Type: New Feature
> Components: Table API & SQL
> Reporter: Timo Walther
> Assignee: Anton Mushin
> Attachments: 1.jpg
>
>
> Calcite's {{AggregateReduceFunctionsRule}} can convert SQL {{AVG, STDDEV_POP,
> STDDEV_SAMP, VAR_POP, VAR_SAMP}} to sum/count functions. We should add, test
> and document this rule.
> If we also want to add this aggregates to Table API is up for discussion.
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